Automatic drilling machine



Dec. 5, 1939.

W. C. DREYER- AUTOMATIC DRILLING MACHINE Filed Dec. 17, 1937 II [III 2 6yet:

INVENTOR W////am CDreyen BY v WITNESSES:

-ATT6RNEY Palmetto. 5,1939

AUTOMATIC DRILLING MACHINE William C. Dreyer, Dallas, Tex assignor toWestinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., acorporation of Pennsylvania ApplicationDecember 17, 1937, Serial No.180,402 2 Claims. (01. 255-19) My invention relates, generally, todrilling machines such as are used in drilling oil and gas wells and,more particularly, to a mechanism for automatically maintaining aconstant pressure on the drilling bit of such machines.

In the operation of drilling machines the most efllc'ient drillingaction takes place at certain pressures of the drilling bit on thebottom, the particular pressure depending upon the nature of the stratumupon which the bit is working. The drilling operation comprises rotatingthe drill bit on the end of lengths of drill pipe joined together andadding lengths of pipe as the bit progresses downward into the earth. Asthe drilling progresses and lengths of drill pipe are added, the weightof the pipe, which is borne by the bit, becomes greater than the mostefflcient drilling pressure. This excessive drill bit pressure may causedamage to the drill bit and may result in the application of such excesstorque to the drill pipe as to damage it.

An object or my invention is to provide a system of control which shallfunction to maintain a constant drilling pressure on the drill bit of adrilling machine.

Another object of the invention is to provide a control system for anearth drilling machine which shall function to maintain a predeterminedpressure on the drill bit and which may be adjusted to so compensate iorthe addition of drill pipe as to maintain the desired drill bit pressureregardless of the amount of drill pipe added.

These and' other objects and advantages of the invention will beapparent from the following detailed description taken in connectionwith the accompanying drawing in which the single figure is adiagrammatic representation of the preferred embodiment of my inventionshowing the cooperative relationship of the various elements of theinvention.

In practicing my invention, I provide a torque motor formaintaining aback tension on the drill pipe suspending sheave tackle. This backtension is provided by the stalled torque of the torque motor and isvaried at will to give the desired net drill bit'pressure by varying theimpedance in the rotor circuit of the motor to vary the stalled torqueof the motor. Thus when an additional length of drill pipe is connectedthe additional weight added thereby is compensated for by decreasing thetorque motor rotor circuit im edance to produce a higher motor stalledtorque and hence a higher'back tension on the dril. pine suspendingtackle. By the same method the stalled torque may be varied to vary thedrill bit pressure when. desired to provide the proper drill bitpressure for the various strata of earth encountered by the drill. I

- Referring now to the drawing, I have shown a drill stem 2 of adrilling machine such as is commonly used in drilling oil and gas wells,having the usual block and tackle hoisting equipment 4 connectedthereto. A tension measuring'device 6 may be connected in the dead endof the tackle and the other end of thetackle is wound on a drum 8 whichis mechanically connected to the rotor of the motor I0 in any suitablemanner.

The motor I0 is a three-phase wound rotor induction motor having rotorwinding taps I2, I4 and IS. The tap I2 is connected through resistanceelements I8, 24, 30, 36 and 42 in series circuit relation, to the commonconductor 48. The tap I4 is connected to the common conductor 48 throughthe resistances 20, 26, 32, 38 and 44 in series circuit relation. Thetap I6 is connected to the common conductor 48 through the resistanceelements 22, 28, 34, 40 and 46 in series circuit relation. Thecontroller 50 has step contacts arranged to cooperate with contactpoints 52 through 82 to provide shorting or shunting circuits for theindividual resistance elements l8 through 46 to successively decreasethe resistance in the rotor circuit of the motor ID as the controller'50 is moved in' the direction indicated to successively engage thecontact elements 52 to The drill stem 2 is rotated by the usual beveledgear arrangement 84 which is driven by a suitable motor 86. Motor 86maybe connected by any suitable circuit breaker 88 to a suitable sourceof alternating current power through conductors X, Y and Z, shown. Arelay 90 is connected by conductors 92 and 94 to one phase of thealternating current power source on the motor side of the circuitbreaker 88. The contact element 96 of relay 9B is normally biased to theclosed circuit position and is connected in series circuit relation withthe coil of relay 98 to complete an energizing circuit for relay 98which extends from the conductor X through conductor I00, the coil ofrelay 98, conductor I02, contact element 98 and conductor I04 to theconductor Y. The contact elements I06 and I08 of relay 98 are biased tothe open circuit position and are arranged to close a circuit betweenconductors III) and H2 and H4 and H2, respectively, when the coil ofrelay 98 is energized to provide shorting circuits for the taps I2, I4and i6 and to thereby cut 3 out the external resistance in the rotorcircuit of motor 10.

In the operation of the device, the controller 50 may be moved to theright to cut out substantially all of the-resistance in the'rotorcircuit of motor l0, thenwith the circuit breaker 88 in the open circuitposition, it will be seen that relay 98 will be energized and itscontact elements I06 and I08 will be moved to the closed circuitposition to provide a shorting circuit for the taps l2, I4 and 16 of therotor circuit. -Under these conditions, the motor I will be exerting itsmaximum torque and will be providing its maximum lifting 'force on thedrill stem 2.. The pressure on the drill bit willbe a minimum underthese condi tions. If, now, circuit breaker 88 is moved to the closedcircuit position, motor 86 will be started and the drill pipe 2 will berotated to perform the drilling operation. With the closure of circuitbreaker 88 the coil of relay 90 will be energized to cause the movementof its contact element 95 to open circuit position to in turn deenergizethe coil of relay 98 and cause its contact elements to open thehereinbefore described shorting circuits of the rotor winding. Underthese conditions the torque exerted by the motor ID in its stalledcondition will be determined by the amount of resistance in its rotorcircuit, and this, in turn, will be determined by the position of thecontroller 50. The tension indicating device 6 may be calibrated toindicate-the lifting force exertedon the drill ipe 2 by the motor l0. Bysubtracting the indicated force from. the known weight of the drill pipe2, the amount of pressure on the drill bit may be obtained. If, now, itis desired to apply a particular pressure to the drill bit, thecontroller 50 may be adjusted to connect such resistances in the rotorcircuit of motor I0 as will cause the tension indicator 6 to indicatethe difference between the total known weight of drill stem 2 and thepressure which is desired to apply to the drill bit.

It will be'seen that with the controller 50 properly set to cause motorIll to exertsuch a stalled torque as will provide a desired pressure onthe drill bit, this desired pressure will be maintained constant so longas the total length of. drill pipe remains the same and the torque motorwill per mit the drill pipe to be lowered as the hole is drilled formaintaining the drill bit pressure substantially constant.

If, now, it is desired'to apply a different drill bit pressure becauseof .the change in the nature of the stratum upon'which the drill bit isworking, the controller 50 is adjusted to supply a stalled torque formotor In which will provide a lifting force on the drill pipe 2 which isthe difference between the weight of the drill pipe 2 and the desireddrill bit pressure.

As the drilling operation progresses and it becomes necessary to addlengths of drill pipe, the total drill pipe weight will increase, and,if it is desired to maintain the same drill bit pressure before andafter adding lengths of drill pipe, it is only necessary to adjust thecontroller 50 to decrease the rotor' circuit resistance such an amountas will result in a motor torque sufiicient to supply a lifting force.on the drill pipe equal to the difference in the new total weight ofthe drill pipe and the desired drill bit pressure.

It will be apparent that a constant pull on the drill may be maintainedwhile the drill is being pulled up'and the hole is being reamed. Withsuch constant pull upon the drill, it will be seen -that the drill willfeed up at a rate depending upon the ease of cutting of the stratumthrough which it is passing. To provide the desired pull, the motortorque is adjusted by means'of the controller 50 to provide a pull onthe drill stem which is greater than the drill stem weight by the amountof net pull that it is desired to exert upon the drill.

It will be seen that I have provided a system for establishing andmaintaining a constantdrill bit pressure for a drilling machine whichmay be adjusted to provide the desired drill bit pressure for any givenlength of drill pipe, which may be adjusted to maintain a desired drillbit pressure for different lengths of drill bit, pipe, which ismerelyillustrative of the principles of my invention.

I claim as my invention:

1. In a system for controlling the pressure on the drill bit of an earthboring machine having a drill stem and a drill bit, means including amotor for rotating'the drill bit, a wound rotor induction motorconnected to tend to hoist the drill stem in the stalled condition ofthe induction motor, means for selectively varying the resistance in therotor circuit of the motor to vary the stalled torque of the motor, andmeans responsive to the deenergization-of the drill rotating motor fordecreasing the resistance in the rotor circuit to increase-the inductionmotor torque.

2. In a system for controlling the drill stem -of an earth boringmachine having drill stem rotating means and drill stem' lifting means,means for causing the lifting means to provide lifting forces of twodifferent values, and means for automatically causing the greater of thetwo lifting forces to be applied to the drill stem while the rotatingmeans is not actuated and for causing the lesser of the two liftingforces to be applied to the drill stem while the rotating means isactuated. I

WILLIAM C. DREYER.

